Shielding means for radio apparatus



July 3, 1934. H. E. ROYS I SHIELIDING MEANS FOR RADIO APPARATUS Filed March 31, 1933 TTOEIVE K Patented July 3, 1934 UNITED STATES PATENT OFFICIE Henry E. Roys, Haddon Heights, N. J., assiguor to Radio Corporation of America, a corporation of Delaware Application March 31,

18 Claims.

My invention relates to shielding means for radio apparatus and particularly to shielding means for vacuum tube apparatus such as high frequency vacuum tube amplifiers and the like.

In building low priced receiving apparatus, it is desirable to reduce the cost of shielding the vacuum tube amplifier stages thereof and, at the same time, to make the apparatus as compact as possible. Since high gain tubes, such as screen grid tubes, are commonly employed therein in order to obtain suflicient amplification with a small number of tubes, the shielding must be very effective.

Furthermore, in building high frequency radio apparatus, such as high frequency receivers and oscillators, for example, it is also desirable and necessary to reduce the length of high frequency circuit leads to simplify the shielding and to provide a simple, compact arrangement of circuit elements associated with the vacuum tube amplifier devices.

It is, therefore, an object of my invention to provide improved and simplified shield means for a vacuum tube amplifier device, and input and output circuit coupling elements associated therewith.

A further object of my invention is to provide an electric circuit impedance or coupling device adapted to be mounted directly upon a vacuum tube terminal whereby it may be included in common shield means with the tube.

A further object of my invention is to provide a common shield for an amplifier tube and its grid or input inductance coil.

A still further object of my invention is to so arrange the radio receiver parts that the leads having high radio frequency potentials will be short.

A still further object of my invention is to so arrange and shield the circuit elements of a vacuum tube amplifier that the amplifier will be 1933, Serial No. 663,703

Fig. 4 is a circuit diagram of the apparatus shown in Fig. 1.

Referring to Fig. 1, a preferred embodiment of my invention comprises a stepped base member having the amplifier tubes (the first tube being the tube 11) mounted upon the lower step, and a gang condenser 12 mounted upon the upper step. The tubes are of the screen grid type having a control grid terminal 13 at the top of the tube.

The base 10 is preferably provided with a brace or supporting angle plate or member '7 upon which may be mounted some of the receiver units such, for example, as a variable resistor 8.

In accordance with one of the main features of my invention, an impedance element for a vacuum tube circuit is adapted to be connected directly to a terminal of a vacuum tube with which it is associated in circuit, whereby connection leads between said element and the terminal are eliminated or reduced to a minimum length and common and simplified shield means may be employed for both. In the present example an inductance coil 14 is mounted on top of the tube 11 in direct connection with the terminal .13. The coil is a grid inductor and the terminal 13 is the grid terminal of the tube. Preferably, a solenoid coil is employed, which has a terminal sleeve 15 mounted inside the coil at the lower end, as shown more clearly in Fig. 2. The sleeve 15 is designed to fit snugly over the grid terminal 13 to form both a support for the coil and a short connection between the lower terminal of the coil 14 and said grid terminal.

Other amplifier tubes (not shown) at the rear of the tube 11, as viewed in Fig. 1, may have their grid inductance coils mounted in the same manner.

The gang condenser 12 comprises a plurality of tuning units, these units being shielded from each other by means of a grounded shielding plate 17. Each unit comprises stator plates 18 mounted upon strips 19 of insulating material, and rotor plates 20 which are connected to ground, 1. e. to the condenser frame and the base 10. The lower terminal of the grid inductance coil 14 is connected to the stator plates 18 of one of the tuning units through a lead 16, while the upper terminal of the coil 14 is connected to the grounded rotor plates 20 through a short lead 21 connected to the shielded plate 1'7. The terminal connections, under certain conditions may, of course, be reversed.

A shield 22 is provided which is common to the amplifier tube 11 and its grid or input coil 14.

The shield 22 comprises a lower tubular, and prefierably cylindrical, portion 22a which substantia ly surrounds the vacuum tube 11, and an upper removable cover portion 22b which substantially surrounds the inductance coil 14.

The cover portion 22b has a slot 23 in one side, near the lower edge, through which the condenser leads 16 and 21 extend. The complete shield 22 in the cylindrical form illustrated, is mounted upon the lower step of the base 10 by means of a screw-threaded engagement with a threaded cap 24 secured to and carried by the base. In the present example it is riveted to the base as indicated in Fig. 1.

An output choke coil 25, which is connected in the plate circuit of the tube 11 to form one unit of the output coupling circuit therefor, is mounted upon a stud 26 extending from the lower side of the base 10, preferably directly beneath the vacuum tube 11 and coaxial with the tube and the shield 22. A separate cup-shaped shield member 27 surrounds the choke coil 25. It is held in place on a threaded extension 9 of the stud 26 by a nut 6. Thus it will be seen that the grid inductance coil 14, the vacuum tube 11, and the plate choke coil are arranged coaxially in a compact manner, yet the coils are adequately shielded from each other.

The circuit for the amplifier is shown in Fig. 4. Only two amplifier stages are illustrated, each stage comprising a screen grid tube having an indirectly heated cathode. The input circuit for the first amplifier 11 comprises the inductance coil 14 and a variable condenser 28 which is one unit of the gang condenser 12. The input circuit of the second amplifier tube 29 comprises a similar inductance coil 30 and a variable condenser 31 which is another unit of the gang condenser 12. The lower terminal of the inductance coil 14. is connected to the control grid 32 of the vacuum tube 11 through a short grid lead 33 which, in Fig. 1,. is the terminal sleeve 15. The upper terminal of the inductance coil 14 is connected to ground through the shielding, and from ground to the cathode 34 through a gridbiasing resistor 35. The resistor is shunted by a radio frequency by-pass condenser 36. The preferred connection for the upper terminal of coil 14 is the one shown in Fig. 1, where it is connected to the shield 17 but, if desired, it may be connected to the shield 22 as indicated in Fig. 4.

The lower terminal of the inductance coil 30 is connected to the control grid 37 of the vacuum tube 29 through a short grid lead 38 which is a terminal sleeve such as 15 shown in Fig. 1-. The upper terminal of the inductance coil 30 is connected to the cathode 39 through the grounded shield and base, and a biasing resistor 40, as in the first amplifier stage. This biasing resistor 40 also is shunted by a radio frequency by-pass condenser 41. The plates 42 and 43 of the vacuum tubes 11 and 29, respectively, are supplied with positive potential through the choke coils 25 and 45. The plate 42 of the first tube is coupled to the input circuit of the second tube by means of a coupling condenser 46. The plate 43 of the second tube also is coupled to the next stage by means of a coupling condenser 47.

The dotted lines in Fig. 4 indicate the shielding of the apparatus. It will be apparent that the vacuum tube and input coil of one amplifier stage are enclosed in a common shield and that the choke coil 'and coupling condenser of this same amplifier stage are in a separate shield. In this arrangement, the coupling condenser 46 and the plate lead 49 between the plate 42 and the choke coil 25, are completely shielded by means of the shield 27 mounted underneath the vacuum tube 11.-

It will also be apparent that between amplifier stages there is only one lead (lead 48) which is at high radio frequency potential. I

A modified form of my invention is shown in Fig. 3 where a different type of screen grid tube is emplbyed. The design shown in Fig. 1 is suitable for use with a tube in which the screen grid surrounds the plate. In case a type of screen grid tube is employed in which the screen grid does not surround the plate, the form of shielding shown in Fig. 3 is desirable. In the type of tube just mentioned, a screening element 50 is pro-- vided in the topof the tube. In accordance with my invention an additional screening element 51 is provided which slips over the end of the tube to cooperate with the screening element 50 and the screen 22 to completely screen the inductance coil 14 at the top of the tube and isolate it from the other tube elements. y

Also, it may be desirable to support the inductance coil from the upper screen portion 221), as illustrated in Fig. 3, instead of supporting it solely from the grid terminal of the tube.

Various other modifications may be made in my invention without departing from the spirit and scope thereof, and it is desired that only such limitations be placed thereon as are necessitated by the prior art and as are set forth in the appended claims.

I claim as my invention:

1. An inductance coil having a terminal sleeve mounted thereon and providing one terminal of said coil, said coil being adapted to be mounted on a vacuum tube with said terminal sleeve iltting over a terminal thereof.

2. In combination, a vacuum tube having a terminal at an end thereof, an inductance coil, and terminal means for said coil connected with said tube terminal to support the coil on said tube.

3. In combination, a vacuum tube having a. terminal at an end thereof, and'an inductance coil mounted coaxially therewith, one terminal of said coil being connected to said terminal and forming a support for the coil.

4. A solenoid inductance coil having a terminal sleeve mounted at one end of said coil and connected to an adjacent end of said coil winding, said coil being adapted to be mounted on a vacuum tube coaxially therewith, the terminal sleeve being adapted to engage a terminal of the tube to form the sole support for said coil.

5. Incombination, a shield base, a vacuum tube socket associated with said base, a tubular metallic vacuum tube shield mounted on said base and extending from said socket on one side thereof, a detachable cover member for said 185 shield, and a circuit coupling coil within said shield and associated with said cover member.

6. In combination, a vacuum tube shield having an opening for a vacuum tube terminal, a cover for said opening, and a coupling device 140 associated with said cover and adapted to be attached directly to said terminal.

7. In combination, an impedance device for a vacuum tube circuit having a terminal adapted to engage and connect with a terminal of a vac- 145 uum tube, and a shield comprising an open shield section for receiving a vacuum tube, anda cover portion therefor associated with said impedance device.

8. In combination, an impedance device for a 15 vacuum tube circuit having a terminal adapted to engage and connect with a terminal of a vacuum tube, a base provided with a vacuum tube socket, and a shield comprising an open shield section for receiving a vacuum tube when mounted in the socket, and a cover portion therefor associated with said impedance device.

9. In radio apparatus, the combination of a vacuum tube having a control grid terminal at the top thereof, an inductance coil having a terminal sleeve mounted on said coil and connected to an end of the coil winding, said coil being positioned above said tube with said terminal sleeve fitting over said control grid terminal, a shield common to. said tube and said coil, said shield comprising a portion surrounding said tube and a removable cover portion surrounding said coil, said coil being mounted on said cover portion and being removable therewith.

10. In radio apparatus, the combination of a vacuum tube having a control grid terminal at the top thereof and having a shield in the upper end thereof, an inductance coil having a ter-' minal sleeve mounted on said coil and connected to a terminal of said coil, said coil being positioned above said tube with said terminal sleeve fitting over said control grid terminal, a shield common to said tube and said coil, said shield comprising a portion surrounding said tube and a removable cover portion surrounding said coil, and a shield fitting over the top of said tube adjacent to said first-mentioned shield and making contact with said first-mentioned shield portion to form a shielding partition between said coil and the tube electrodes.

11. Radio apparatus comprising a vacuum tube having a terminal at the top thereof, an inductance coil mounted above said tube coaxially therewith, one terminal of said cell being connected to said terminal, and a single shield surrounding said vacuum tube and said inductance coil.

12. In an amplifier, a vacuum tube having a control grid terminal at the top thereof, a tunable input circuit for said vacuum'tube comprising a tuning inductance coil, said coil being mounted above said tube and having one terminal connected directly to said control grid terminal, and a shield enclosing both said coil and said first tube and its input inductance coil, and

a shield surrounding said second tube and its input inductance coil, the variable condensers for said input circuits being units of a gang condenser positioned at one side of said tubes.

14;. A high frequency amplifier having a first tube and a second tube, the second tube having a tunable input circuit including a tuning inductance directly connected with a tube terminal, means including an impedance element and a coupling condenser for coupling the first tube to said input circuit, a shield enclosing the second tube and said tuning inductance, and a third shield enclosing said impedance element and coupling condenser. a

15. In an amplifier, a first vacuum tube and a second vacuum tube, said second tube having a control grid at the top thereof and having a tunable input circuit comprising an inductance coil shunted by a variable condenser, said induct-ance coil being mounted above said tube and having one terminal connected to said control grid terminal, means including an impedance coil in the plate circuit of said first tube for coupling the plate of said first tube to the input circuit of the second tube, an impedance coil in the plate circuit of said second tube, a shield surrounding said first impedance coil, a shield surrounding said second impedance coil, and a shield surrounding said second tube and said inductance coil.

16. In an amplifier, a vacuum tube having a control grid terminal at the top thereof, a tunable input circuit for said vacuum tube comprising an inductance coil shunted by a variable condenser, said coil being mounted above said tube and coaxially therewith and having one terminal connected to said controlgrid terminal, a shield common to said tube and said inductance coil, a second vacuum tube, means for coupling the output of said first tube to the input of said second tube, said means including an impedance coil in the plate circuit of said first tube, said impedance coil being mounted below said tube and coaxially therewith, and a second shield for said impedance coil.

17. In an amplifier, a stepped metal base, a first vacuum tube and a second vacuum tube, each tube having a control grid terminal at the top thereof, each tube having a tunable input circuit comprising an inductance coil shunted by a variable condenser, the 'coil of the input circuit for said first tube being mounted above said first tube, the coil of the input circuit for said second tube being mounted above said second tube, means for coupling the output circuit of said first tube to the input circuit of said second tube, a shield common to said first tube and the coil mounted above it, and a shield common to said second tube and the coil mounted above it, the variable condensers for said input circuits being units of a gang condenser mounted on the upper step of said base, said tubes being mounted on the lower step of said base.

18. In an amplifier, a'vacuum tube, an input coil and an output coil therefor, said input coil,

said vacuum tube, and said output coil being ar- 1 

